The present invention relates to a reduction gear type starter motor for an internal combustion engine and more particularly to an improvement in a starter motor for an automobile engine wherein a planetary type reduction gear is installed.
One of the typical starter motors of this kind as has been hitherto known as shown in FIG. 1 of the attached drawings. In FIG. 1 there is shown a starter motor 1 of this kind having a planetary type reduction gear, a direct current motor 2, and a field system 3 of motor 2 comprising a cylindrical yoke 4 and poles 5 secured to the inner periphery of yoke 4, poles 5 being permanent magnets, a rear bracket 6 secured to yoke 5 at its rear end and a ball bearing 7 mounted to the inner periphery of the protrusion 6a projected outwards from rear bracket 6 centrally thereof rotatively supporting the rear end portion of the rotary shaft 9 constituting a part of armature 8. Also part of direct current motor 2 is a commutator 10 fit on rotary shaft 9, an armature core 11, armature coils 12 mounted in the grooves of armature core 11, the lead wires thereof 12a being connected to commutator 10, brushes 13 in sliding contact with commutator 10, and thrust washers 14, 15 and 16. A spur gear 17 is mounted on the forward portion of rotary shaft 9 which is in mesh with planetary gears 18 of a planetary type reduction gear so that the torque of armature 8 is transmitted to gears 18. A ring-gear 19 (internal gear) fits together with a flange 20 into the annular groove 21a of an intermediate bracket 21 which is in turn connected to yoke 4 through a faucet joint, groove 21a constituting a part of thereof. An overrunning clutch 22 is connected to an output rotary shaft 23 by splines and adapted to be energized by the revolution of planetary gears 18. A pinion 24 is fixedly secured to overunning clutch 22 and adapted to be rotated in one direction only. A shift lever 25 engages overrunning clutch 22 so as to shift it forward. A front bracket 26 mounts a sleeve bearing 27 in the inner periphery of its forward end portion centrally thereof, bearing 27 rotatively supporting the forward end of output rotary shaft 23. A stopper 28 is provided to constrain the excessive forward movement of overrunning clutch 22. A thrust washer 29 is provided to bear thrust load generated in output rotary shaft 23. Also provided is a grommet 30, one end of which is born against a magnetic switch 31 and carries the pivotal part of shift lever 25 between it and the inner protruded portion 26a of front bracket 26 so as to put the rotary part therebetween. Intermediate bracket 21 has its rear end connected to yoke 4 through the faucet joint as above described, the front end being connected to front bracket 26 through a faucet joint as well, whereby intermediate bracket 21 and yoke 4 are held in position by through bolts (not shown) passing through near the inner peripheries of rear bracket 6, yoke 4, intermediate bracket 21 and front bracket 26 from rear bracket 6 to front bracket 26 with the ends of the bolts being secured to both brackets 6 and 26, respectively, as by screwing.
The conventional reduction gear starter motor having such a constitution as above stated operates as follows:
Energization of magnetic switch 31 operates shift lever 25 to move overrunning clutch 22 forward so that thereby pinion 24 is caused to mesh with a ring-gear (not shown) of an internal combustion engine, and succeedingly the main contacts (not shown) of magnetic switch 31 are closed and a voltage is applied to brushes 13 from an electric current source (not shown) to cause an electric current to flow through armature 8, to cause armature 8 to rotate and torque to be transmitted to planetary gears 18 through spur gear 17 mounted to rotary shaft 9, whereby torque is transmitted further through the route of output rotary shaft 23, overrunning clutch 22 and pinion 24 in this order under the decrease of the rotational speed, the torque finally transmitted to the internal combustion engine through pinion 24 and the ring-gear now in mesh with each other. Although the representation is omitted in FIG. 1, the front end of rotary shaft 9 of armature 8 is rotatively carried by output rotary shaft 23, the rear end of which is rotatively carried by flange 20, with necessary machining accuracies being maintained between the relative rotational parts.
From the foregoing, it will be apparent that the conventional starter motor has various defects in that the brackets to rotatively support rotary shaft 9 are constituted separately, and in particular, intermediate bracket 21 is a fundamental factor in reducing the accuracy of alignment of the bearing portions of rotary shaft 9 and output rotary shaft 23. It is a further drawback of the conventional starter motor that it requires a considerable number of constitutional elements, bring about disadvantages in manufacturing costs, etc.